1. Field of the Invention
The present invention is generally related to a method and system for determining a grip or grasping pattern of a prosthetic terminal device or other orthotic device using the position of the thumb or other digit as the initial determination of the grasping function.
2. Description of the Related Art
In the field of prosthetics, electrically powered terminal devices such as hands and hooks, have limited functionality, which usually consists of the open and close positions. In general, the thumb, index and middle fingers are mechanically connected together and act in one motion. The ring and pinky fingers are passive and have no gripping capability. These terminal devices do not allow individual movement of the digits. In order to operate the prosthetic devices, the patient typically has one or two control sensors to operate the open and close motion. These are usually configured so that one sensor controls each movement. Such a sensor is usually referred to as a patient sensing device or PSD and may be placed on the forearm of a patient to sense myoelectric signals in the forearm and determine whether to open or close the device. For example one sensor opens the terminal device while a second sensor closes the terminal device.
While the above discussed system works well for terminal devices without individual movement of digits, new electric terminal devices that have individual digit control such as devices that have at least one motor or drive mechanism per digit, pose new challenges to the control system and the patient interface. Since such a device uses multiple digits in multiple positions, this type of terminal device could be positioned in an infinite number of positions. While this new terminal makes the movements more robust than previous devices that limit movement to certain limited positions, it provides difficulties in using the existing two sensors to get accurate information from the patient to determine the exact position requested from the vast array of positions now available. In order to control such devices, additional sensors have been used to monitor the patient's myoelectric signals in order to more accurately calculate the proper movements of the terminal device or its parts. Since more control from the patient is required, this means adding many sensors or complex control systems to interpret the patients' desired action. This is both cumbersome and inconvenient to the patient as well as more complex from an electrical perspective resulting in more errors in controlling the device.
It would therefore be desirous to have a system and method of controlling a prosthetic device using a limited number of sensors while still allowing the patient the flexibility of choosing a number of different actions for the prosthesis.